Hard to debug tmt plans ls with remote plans

[lukaszachy]

Scenario: fmf data seems correct, changes are pushed, but tmt plans ls complains with No tree node found for XXX reference.

Culprit was in 'fmf' which caches cloned repo but that is not visible from any log (TMT_DEBUG=1 nor plans --dddvvv print anything).

IMO we need:

• Print debugging info from tmt plans (and possibly others) about what is being done
• Make fmf to emit debugging info from https://github.com/teemtee/fmf/blob/29190c78e4065adf98cbb3ccf747b01973d761e2/fmf/base.py#L659 (and what it calls)

Bonus

• have tmt option/flag to force fetching fresh data (needs fmf feature as well)

[lukaszachy]

Possible reproducer:

$ mkdir -p /tmp/reproducer/remote
$ cd /tmp/reproducer/remote
#  repo contains no plan, just fmf root
$ git init && tmt init && git commit -m just-fmf-root

$ mkdir -p /tmp/reproducer/local
$ cd /tmp/reproducer/local
$ tmt init
$ cat <<EOF > plan.fmf
plan:
    import:
        url: /tmp/reproducer/remote
        name: /foo
EOF
# Expected outcome for this call:
$ tmt p ls

No tree node found for '{'url': '/tmp/reproducer/remote', 'name': '/foo'}' reference
$ cd /tmp/reproducer/remote
$ cat <<EOF > foo.fmf
execute:
  how: tmt
EOF
$ git add foo.fmf && git commit -m added-plan

# Plan addded to the remote, but plan cannot import it...
$ cd /tmp/reproducer/local
$ tmt p ls

No tree node found for '{'url': '/tmp/reproducer/remote', 'name': '/foo'}' reference

# It used cached repo... and at that time /foo was not there.
# There is no way how to see this from debug output
# To see that it works if it does fresh checkout ...
$ rm -rf ~/.cache/fmf/_tmp_reproducer_remote*
$ tmt p ls
/plan